Specification for requirements imposed on adding users to groups. Map of group names to specification arrays, which specify minimum requirements a user must meet to be added to the group. Keys are 'edits' for the minimum number of edits, 'age' for the minimum account age, 'exemptGroups'; for the groups that may add a user ignoring the requirements, and 'reason'; for to override the default message explaining why the group may not be added (uses 'checkuser-group-requirements' by default)